A wide range of industries employ evaporators for concentrating solutions and slurries, including oil refining, synthetic fuel production, food processing, herbicide and pesticide production, electric generating stations, primary metal refining, pharmaceutical production, and pulp and paper manufacture. The evaporators may be used to increase the concentration of a fluid component, and/or to crystallize a solute component. Various types of evaporators are available and are well known in the prior art. An example is a vertical, tube-in-shell, falling film evaporator. In such evaporators, a solution or slurry is circulated repeatedly through heat exchange tubes. As the solution or slurry passes through the heat exchange tubes, the solvent, i.e., water or organic solvent, is gradually evaporated, leaving a more concentrated solution or slurry, and often causing solute components to precipitate.
Evaporators typically include various chambers, apertures, and tubes through which the solution or slurry must pass repeatedly as it is concentrated. Care must be taken to provide for efficient flow of solid particles as well as liquid. Slurries contain solid particles even during initial stages of concentration, while solutions contain solutes, i.e., salts, which may precipitate out of solution during concentration. These solid particles can cause clogging in various parts of the evaporator.
Deposits may occur along the walls or other surfaces of the evaporator. Deposits may break off in the form of chips or flakes, which can cause clogging of the evaporator and interrupt the flow of the solution or slurry to be concentrated. If the system is clogged and circulation cannot proceed efficiently, the system must be shut down to allow operators to clear and clean the blockage.
Deposits occur while the evaporator is in operation and also while the evaporator is shut down for cleaning; as the walls of the evaporator system are allowed to dry out during the cleaning operation, significant amounts of deposits can form. When the system is restarted and circulation is restored, the new deposits often flake off and reclog the system.
The clogging problem is most serious when chips lodge themselves within smaller apertures, such as the inlet orifices of the fluid distributors mounted at the top of heat exchange tubes. One such distributor is described in U.S. Pat. No. 4,248,296. Chips interfere with normal flow of the brine, and can effectively remove entire heat exchange tubes from operation.
Various attempts have been made to remove the chips or flakes by filtration. For example, screens or strainers have been fitted inside the evaporator system. However, such screens must be cleaned periodically, and in order to do so, the evaporator system must be shut down, resulting in lost time, increased costs of operation, and further formation of deposits. In addition, when the evaporator is restarted, additional chips and flakes may form downstream of the screen or strainer, and reclog the system.
It is, therefore, desirable to -design an apparatus which will facilitate separation of solid particles from liquid, and which will not require the system to be shut down for cleaning of the separation apparatus.